In a radio base station, energy consumption of a radio frequency power amplifier accounts for a very high proportion in total energy consumption of the base station device. To reduce energy consumption, a dual-input radio frequency circuit, for example, an outphasing circuit, or a Doherty (DHT) circuit including a primary power amplifier and a secondary power amplifier, is usually used to improve power amplification efficiency. However, when the conventional dual-input radio frequency circuit is used to improve back-off efficiency, efficiency between a power back-off point and a high power point may be reduced significantly. Finally, efficiency of a device, such as the base station, for outputting a modulated wave is affected.
To improve the significantly reduced efficiency of the dual-input radio frequency circuit, in the prior art, a DHT circuit and an outphasing circuit are combined to form a composite radio frequency circuit. That is, the outphasing circuit is used as a primary power amplifier of the DHT circuit, and then a secondary power amplifier is added to perform load modulation). The composite radio frequency circuit can effectively improve the significantly reduced efficiency of the dual-input radio frequency circuit between the power back-off point and the high power point. However, a quantity of input signals of the dual-input radio frequency circuit is increased from original two to three, and consequently a size of the entire composite radio frequency circuit becomes excessively large. In addition, to provide three input signals to the composite radio frequency circuit, three transmit channels need to be disposed for the composite radio frequency circuit. Therefore, the composite radio frequency circuit has relatively high use costs, unfavorable to large-scale application and popularization.
To reduce a quantity of transmit channels, in a common prior-art method, signals transmitted on two transmit channels are converted into three input signals by performing an operation such as splitting or combination, and the three input signals are connected to the composite radio frequency circuit. However, after three input signals are obtained by using this method, when the signals transmitted on the two transmit channels are adjusted, at least one input signal cannot be adjusted to an expected value. Consequently, the composite radio frequency circuit at rated power cannot reach optimal power amplification efficiency, and overall performance of the circuit is poor.